A projector having solid state light source that uses a light emitting element such as a light emitting diode (LED) or a semiconductor laser (LD) as a light source has been proposed. A projector having solid state light source of this type has an illumination optical system into which light emitted from the light emitting element enters; a light valve having a display element such as a liquid crystal display panel that light that exits the illumination optical system enters or a DMD (Digital Micromirror Device); and a projection optical system that projects light that exits the light valve to a projection plane.
A requirement for the projector, having solid state light source, is that there be a minimum of optical loss in the optical path from the light emitting element to the light valve so as to improve the luminance of projected images.
In addition, as described in Non-Patent Literature 1, such a projector having a solid state light source is restricted by the etendue that depends on the product of the area and emission angle of the light source. In other words, light emitted from the light source cannot be used as projection light unless the product of the light emission area and emission angle of the light source is equal to or smaller than the product of the area of the incident plane of the light valve and the acceptance angle (solid angle) that depends on the F number of the optical system.
Thus, there has been a demand to reduce the etendue of light emitted from the emitting element so as to reduce the foregoing optical loss.
Projectors having solid state light source for business use and home theaters need to emit a light beam in the order of several thousand lumens. Thus, such projectors having solid state light source need to improve the light use efficiency of light emitted from the emitting element and realize high luminance and high directivity.
As an example of a display element having a light source with an improved light use efficiency, as shown in FIG. 1, a spatial optical modulator that has an MEMS (Micro Electro Mechanical Systems) shutter mechanism that selectively shades incident light emitted from light source 1204 has been disclosed (refer to Patent Literature 1). This display element has light source 1204; optical cavity 1202 into which light 1214 emitted from light source 1204 enters; optical modulation array 1206 that modulates light 1214 that exits optical cavity 1202; and cover plate 1207 that covers optical modulation array 1206.
Optical cavity 1202 has optical guide 1208; and substrate 1210 arranged on optical guide 1208 with air gap 1213. Formed on optical guide 1208 is rear reflection plane 1212 including light scattering elements 1209. Optical modulation array 1206 has light transmitting regions 1222 that light that exits optical cavity 1202 enters; and an MEMS shutter mechanism including shutters 1110 that can open and close light transmitting regions 1222. Cover plate 1207 has light transmitting regions 1114 through which light 1214 that has passed through light transmitting regions 1222 of optical modulation array 1206 passes. In this display element, light 1214 is multiply reflected between shutters 1110 and optical cavity 1202, reuses light 1214, and causes it to pass through light transmitting regions 1222. As a result, the display element improves the light use efficiency of light source 1204.